There are a number of mystic perfections that can be achieved by successful yogis. Although they were far more common in previous ages, some can still be achieved even in Kali-yuga. In essence, all these mystical perfections come into contact with the Supreme Lord in some of His forms or features, therefore devotees can also often achieve these powers, although they will be reluctant to use them.
Krsna is the source of all mystic powers, therefore, one who is strongly connected with Krsna in any of His aspects may start exhibiting such powers, just like a bar of metal in contact with fire becomes hot and acquires the potency of burning. The point is that supernatural powers like this can easily make one proud, and thus make him fall. Yogis are generally conditioned souls, and thus they are anxious to prove themselves, but devotees are the opposite.
In the nectar of devotion, Srila Prabhupada explains that the primary mystic perfections achieved by greatly successful yogīs are eight in number. They are called aṇimā, laghimā, mahimā, prākāmya, prāpti, īśitva, vaśitva and kāmāvasāyitā.
The first one, Aṇimā-siddhi, allows one to become very small and thus enter into hidden or closed places. Just like Paramamtma can enter everywhere, a yogi in possession of this power can also enter everywhere, even inside a stone.
Using laghimā, one can become very light, and thus fly to distant places without difficulty. Once, in a TV interview after disembarking the plane, Srila Prabhupada started describing different ways this siddhi can be used for flying (using a stick, a carpet, etc.) when the reporter asked why then he was flying on American Airlines, he answered: To be one with you! 😆
The highest perfection for this siddhi, however, is to be able to fly in space using the rays of the sun, which work like cosmic roads connecting all different parts of the universe. By this process a yogi can go from his planet to the sun, and from there reach any other part of the universe. Prabhupada mentioned on occasion that he was testing this power at night, traveling in space like the yogis.
Another perfection, mahimā allows the yogi to increase his size and physical power. This mystic perfection is often used by demons while fighting their opponents. Hiranyaksa, for example, was so powerful that could assume a form that was many times bigger than our planet to fight Lord Varahadeva.
By the siddhi called prāpti (acquisition) a yogi can bend space and reach any distant object. Using this power, a yogi can touch or grab objects from distant places (or even distant planets) by bending space and then reaching them by just extending his hand. He can grab a fruit from a tree thousands of kilometers away, or even touch the moon with his finger. By using this perfection one can also enter into the senses of others through the predominating deities of the senses, and thus enjoy anything they enjoy.
By the siddhi called īśitva, a yogi can manipulate the sub-potencies of māyā, and thus create any kind of wonderful material object. Kardama Muni, for example, used this mystical perfection to create a flying castle for Devahuti, which was able to reach the celestial planets. At the highest level, this perfection can be used to even create planets, or annihilate them at will. Krsna is the Supreme Controller, and by mastering his yogic perfection one becomes a smaller controller inside this universe.
By using vaśitva, one can interfere with other’s free will and thus bring others under his control. Just like Maya can seduce almost everyone inside this material world, by using this siddhi a yogi can do similarly. Prabhupada explains that vaśitva works like a type of hypnotism that is almost irresistible. Sometimes, people who achieve a small degree of such power become fashionable gurus or speakers who can bring masses of people under their control, and thus exploit them for their purposes. This however doesn’t have any purpose in spreading Krsna Consciousness, because devotional service implies one deciding to serve Krsna under his own free will. By using vaśitva one can also, conversely, keep himself above the control of the three modes of nature.
Another perfection is prākāmya, by which one can satisfy any desire he or she has under the scope of the laws of nature. He can enjoy any kind of material object, acquire any kind of material knowledge, and so on. This power of achieving desirable things reaches its highest level in the siddhi called kāmāvasāyitā.
The difference is that prākāmya allows one to obtain things that are within the scope of the physical laws, while kāmāvasāyitā allows one to contradict nature and do things that are ordinarily impossible. Saubhari Muni, for example, was able to change the shape of his body, becoming a young and handsome man, and then expand himself into eight forms to simultaneously marry all the eight daughters of King Māndhātā. Another yogi used this siddhi to create a tree that produced men instead of coconuts.
As you can imagine, one can use these mystical perfections to achieve wonderful things in this material world and to enjoy his senses to the highest degree. However, these mystical perfections don’t help one to become free from Maya, and thus devotees are usually not interested in them. On the opposite, these siddhis are more like a test, a temptation that can make one fall and become a separate enjoyer of this material world instead of becoming free from it.
As Srila Prabhupada mentions in the first chapter of the Nectar of Devotion:
“Actually, a pure devotee does not aspire after any of these perfections, because the happiness derived from devotional service in Kṛṣṇa consciousness is so transcendental and so unlimited that no other happiness can compare to it. It is said that even one drop of happiness in Kṛṣṇa consciousness stands beyond comparison with an ocean of happiness derived from any other activity. Thus, any person who has developed even a little quantity of pure devotional service can very easily kick out all the other kinds of happiness derived from religiousness, economic development, sense gratification and liberation.
There was a great devotee of Lord Caitanya known as Kholāvecā Śrīdhara, who was a very poor man. He was doing a small business selling cups made from the leaves of plantain trees, and his income was almost nothing. Still, he was spending fifty percent of his small income on the worship of the Ganges, and with the other fifty percent he was somehow living. Lord Caitanya once revealed Himself to this confidential devotee, Kholāvecā Śrīdhara, and offered him any opulence he liked. But Śrīdhara informed the Lord that he did not want any material opulence. He was quite happy in his present position and wanted only to gain unflinching faith and devotion unto the lotus feet of Lord Caitanya. That is the position of pure devotees. If they can be engaged twenty-four hours each day in devotional service they do not want anything else, not even the happiness of liberation or of becoming one with the Supreme.
In the Nārada Pañcarātra it is also said that any person who has developed even a small amount of devotional service doesn’t care a fig for any kind of happiness derived from religiousness, economic development, sense gratification or the five kinds of liberation. Any kind of happiness derived from religiousness, economic development, liberation or sense gratification cannot even dare to enter into the heart of a pure devotee. It is stated that as the personal attendants and maidservants of a queen follow the queen with all respect and obeisances, similarly the joys of religiousness, economic development, sense gratification and liberation follow the devotional service of the Lord. In other words, a pure devotee does not lack any kind of happiness derived from any source. He does not want anything but service to Kṛṣṇa, but even if he should have another desire, the Lord fulfills this without the devotee’s asking.”